JPH064175B2 - Press molding method - Google Patents

Description

The present invention relates to a press forming method for drawing a plate material,
Particularly, the present invention relates to a press molding method in which wrinkles are not generated and cracks are not generated even when the punch pushing stroke is increased.

[Background technology and matters to be solved]

In a press forming method in which a blank with a wrinkle holding plate is pressed into a die having a molding cavity, and the blank is pushed into the cavity with a punch to draw-form, the pressing force applied to the wrinkle holding plate is generally constant. It does not change during molding.

In such a general drawing process, if the wrinkle holding force is inappropriate, the product is wrinkled or wrinkled, and it is impossible to perform deep drawing. For this reason, conventionally, the maximum drawing depth that can be formed without wrinkling due to various wrinkle pressing forces and wrinkling has been investigated.

FIG. 5 shows a diagram of the maximum drawing depth (punch stroke h) when various kinds of wrinkle pressing force are used.
As shown by molding lines d ₁ to d ₅ in the drawing, these are the limit lines L _B and wrinkles which are obtained by connecting the limit points where the blanks are cracked when the blanks are molded with a constant wrinkle holding force. It is shown by a limit line L _W obtained by connecting the limit points. As shown by the forming lines d ₁ and d ₂ , when the wrinkle holding force H is large, the blank is cracked to limit the maximum depth of the drawing process. On the contrary, when the wrinkle holding force H is small, the forming line d ₄ is formed.
And d ₅ on the blank, which also limits the maximum drawing depth.

A punch stroke h for performing draw forming with a wrinkle holding force H _c corresponding to the intersection of the wrinkle occurrence limit line L _B and the wrinkle occurrence limit line L _W.
Is maximum (h _c ).

Here, when the drawing depth required for the molded product is h ₁ , the condition for pressing the wrinkle which can be molded can be adopted from H _L above and below H _c to H _M. However, when the required drawing depth is larger than h _c , the molding is impossible.

In order to further improve this drawing depth, it is necessary to modify the mold and change the blank shape, size and material, which necessitates modification of the mold and modification of the blank shape, and obtains a press-formed product of the desired shape. It can be difficult.

In addition, as a method of changing the force that presses the blank during molding, arrange multiple blank pressing parts, detect the amount of blank drawn in at the position corresponding to this, and set the blank so that it becomes the same as the good product. A device for changing the pressing force of the pressing portion has been proposed (Japanese Patent Laid-Open No. 59-1592).
No. 28).

However, this device is for stable molding, and does not positively expand and improve the drawing limit depth.If a larger molding depth is required, the mold correction and Pilot press work is required to change the blank.

In view of the above facts, it is an object of the present invention to obtain a press molding method capable of press molding without causing wrinkles or cracks even when the punch pushing step becomes large.

[Outline and Action of Invention]

In the press-molding method according to the present invention, a blank is pressed with a wrinkle holding plate to the tie that forms the molding cavity, and the blank is pressed into the cavity with a punch, and the press-molding method is a pressing method at the start of molding. The blank pressing force of the wrinkle presser plate is set higher than the pressure corresponding to the intersection of the wrinkle generation limit line and the wrinkle generation limit line when the blank pressure is constant, and this pressure is increased during punching as the punch pressing amount increases. It is characterized in that the pressure is reduced in a state where it does not intersect with the line and the pressure is made lower than the pressing force corresponding to the intersection at the end of molding.

As a method of reducing the pressing force during molding, the pressing force may be linearly decreased with a constant slope as shown by the molding line d ₆ in FIG. 1, or the decrease rate may be changed on the way as shown by the molding line d _7. It can be made linear, can be changed into a continuous curved line as shown by the forming line d ₈ , or can be reduced by appropriately combining these straight lines and curves.

In this way, if the wrinkle holding force at the initial stage of molding is increased and the wrinkle holding force is reduced as the punch stroke progresses, even if the wrinkle holding force during forming is reached, the limit value for wrinkling will be reached. Wrinkles do not occur. As shown by molding lines C _{1 to} C ₄ in FIG.
When the wrinkle pressing force H is reduced, the wrinkle detection limit line L _W becomes L
_Because it was found to move to _W1 . On the other hand, the crack occurrence limit line L _B does not move despite the change in the wrinkle pressing force.

Therefore, since the forming limit line clamp pressure H _F in the forming end As is clear from Figure 1 have not to wrinkle area when a certain molding initial blank-holding force is not moving, clamp pressure H _F is H _C There is no effect unless it is below. On the other hand, since the wrinkle holding force H _S at the initial stage of molding can be expected to be effective by reducing the wrinkle holding force from the initial stage of molding to the final stage of molding, H _S must be larger than H _C. .

Further, in the process of reducing the wrinkle holding force during forming, as the wrinkle holding force near the wrinkle holding limit line L _W when the wrinkle holding force is constant as in the forming lines C _{1 to} C _{3 in} FIG. Since the depth that can be formed without doing so is large, it is preferable to increase the wrinkle holding force so that it does not come into contact with the crease generation limit line L _B.

Even when the wrinkle pressing force is reduced and drawing is performed, wrinkles will be generated if the forming line indicating that the punch stroke proceeds to some extent intersects with the moved wrinkle limit line L _W1. The reduction rate of the force is changed as shown by the forming line C _{6 in} FIG. 2, that is, the reduction rate of the wrinkle holding force is reduced to continue the drawing without reducing it, and the drawing depth can be further increased. .

Generally, there are many kinds of shapes of molded products, and deformation such as drawing, overhanging, and bending is performed according to this shape, so the wrinkle holding force of each deformed part is controlled accordingly. .
When the entire molded product is deformed by drawing, the dies and the crease presser plate are integrated to apply a crease presser force, and the overall control for controlling this is performed.

On the other hand, when at least a part of the molded product is deformed by drawing, at least a part of either the die or the wrinkle holding plate, or a wrinkle holding force acting on at least a part of both is individually loaded, Partial control is performed. However, even if part of the molded product is deformed by drawing, if the part of this drawing deformation is more important than other parts, even if only part of the drawing deformation is Can also be controlled integrally.

Example of Invention

(Example 1) As shown in FIG. 3, a blank 14 is mounted on a die 12 provided with a molding cavity 10 and the blank 1
The periphery of 4 is pressed by the wrinkle pressing plate 16 and the blank 14 is pressed by the punch 18. This causes the punch 18 to draw the central portion of the blank 14 into the molding cavity 10.

The punch 18 has a diameter of 40 mm, the shoulder radius is 8 mm, the forming cavity 10 has a diameter of 42.5 mm, and the shoulder radius is 8 mm.

The blank 14 had a diameter of 90 mm, and for lubrication with the mold, cleaning rust preventive oil was applied to the surface of the blank 14 and placed on the die 12, and the punch 18 was driven by hydraulic pressure.

Molding is performed under various conditions of constant wrinkle holding force during forming, and the wrinkle generation limit line L _B and wrinkle generation limit line L _{W are} generated.
I asked. Wrinkle pressing force H _{C at the} intersection is 390 kg
Met.

Next, the blank 14 was pushed into the molding cavity 10 by the punch 18 so that the initial wrinkle holding force H _S was set to 1200 kg so that the wrinkle holding force during forming decreased while crossing this H _C.

The punch speed was set to 4 mm / min, and the wrinkle holding force H was linearly reduced at a rate of 36.7 kg / mm as the punch 18 was pushed (see forming line D _{1 in} FIG. 4). Punch stroke is 30.
Flange wrinkles occurred at 2mm, but 29.2
Molding was possible without occurrence of cracks up to mm and cracks.

On the other hand, for comparison, the maximum forming depth h _C when forming with the wrinkle pressing force during forming being constant is 27.0 mm. Therefore, in the present embodiment, this enables deep drawing by 2.2 mm. It was

That is, the molding line D ₁ shows that, when the molding is performed until just before the wrinkle is generated, the punching stroke can be increased more than the conventional molding method without generating the wrinkle or the crack.

(Example 2) Using the same mold, blank, lubrication, and punch speed as in Example 1, the reduction ratios of the initial wrinkle holding force H _S and the wrinkle holding force H were made the same, and the reduction ratio was changed in the middle of molding to perform drawing. Molded.

After passing through the wrinkle limit line L _W when the wrinkle holding force is constant,
Before wrinkling, that is, when the punch pressing amount h is 26 mm and the wrinkle holding force H is 247 kg, the wrinkle holding force is reduced as it is. The limit point of wrinkling (see forming line D ₁ in FIG. 4). The tip stroke is 37 mm when the punching process is carried out so as to avoid the occurrence limit line L _B , that is, the wrinkle holding force H is kept constant (see forming line D ₂ ).
No wrinkles were generated, and it was possible to reduce the aperture by 10 mm more than when the wrinkle holding force was constant.

Example 3 The same mold, blank, lubrication and punching speed as in the above example were used. The initial wrinkle pressing force H _S was the same, the punch pressing amount was molded to 14 mm with the wrinkle pressing force H kept at the initial value, and then the curve was reduced along the wrinkle limit line (see FIG. 4, forming line D ₃ ). .

As a result, the drawing depth is up to 37 mm, no wrinkling occurs, and a drawing depth as large as 10 mm is possible compared with the case where the wrinkle holding force is constant.

(Example 4) Using the same mold, blank, lubrication and punch speed as in Example 1, the initial wrinkle holding force H _S was set to 550 kg, and the punch pushing amount h was set to a constant wrinkle holding force up to 19 mm.
Molded in the same change pattern as in the above (see FIG. 4, molding line D ₄ ).

As in the above embodiment, the drawing depth is up to 37 mm, molding is possible without wrinkling, and the critical forming depth is significantly improved even when the initial wrinkle pressing force H is relatively small close to H _C. I was able to.

(Comparative Example) Using the same mold, blank, lubrication and punch pressing speed as in Example 1, the crease pressing force H _S is smaller than H _C 370.
The pressure was set to kg and the punch was pushed in, and the wrinkle holding force H was reduced at a rate of 16 kg / mm (see forming line D _{5 in} FIG. 4).

In this case, when the punch pressing amount became 16 mm, wrinkles were generated, and wrinkles were generated up to 15 mm, and it was possible to mold without wrinkles, but when molding was performed with the wrinkle holding force being constant at the value of H _C during molding. It was not possible to increase the punch indentation amount of more than 27 mm, and no good result was obtained.

〔The invention's effect〕

As described above, the press molding method according to the present invention, the blank pressing force of the wrinkle holding plate at the start of molding is more than the pressing force corresponding to the intersection of the wrinkle generation limit line and the wrinkle generation limit line when the blank pressing force is constant. It is characterized in that the pressing force is increased during the molding with the increase of the punch pressing amount during the molding so as not to cross the crack occurrence limit line, and at the end of the molding, it is lower than the pressing force corresponding to the intersecting point. In addition to simply reducing the wrinkle pressing force, the blank pressing force is made higher than the pressing corresponding to the intersection of the wrinkle occurrence limit line and the wrinkle occurrence limit line when the blank pressing force is constant,
During the molding, the pressing force is decreased with the increase of the punch pressing amount without crossing the breakage limit line, and at the end of the molding, the pressing force is lower than the pressing force corresponding to the intersection point.
Even if the punch pushing step becomes large, there is an excellent effect that press molding can be performed without generating wrinkles or cracks.

[Brief description of drawings]

1 and 2 are diagrams of wrinkle pressing force with respect to a punch stroke for explaining the present invention, FIG. 3 is a sectional view of a molding die used in the first embodiment, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a diagram showing the wrinkle holding force with respect to the punch stroke, and FIG. 5 is a diagram showing the wrinkle holding force with respect to the punch stroke in the conventional press molding. 10 ... Molding cavity, 12 ... Die, 14 ... Blank, 16 ... Wrinkle retainer plate, 18 ... Punch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-9526 (JP, A) Jikkou 44-12781 (JP, Y1)

Claims (2)

[Claims] 1. A press molding method comprising pressing a blank with a wrinkle holding plate to a die having a molding cavity and pressing the blank into the cavity with a punch to draw-form the wrinkle holding plate at the start of molding. The blank pressing force is made higher than the pressing force corresponding to the intersection of the crease occurrence limit line and the crease occurrence limit line when the blank pressing force is constant, and this pressing force becomes the crease occurrence limit line as the punch pressing amount increases during molding. A press molding method characterized in that the pressure is reduced in a state where they do not intersect, and at the end of molding, the pressure is lower than the pressing force corresponding to the intersection. 2. The pressing force reduction during the molding is characterized in that the pressing is carried out after passing through a wrinkle generation limit line when the blank pressing force is constant, and then the reduction ratio is reduced or not reduced. The press molding method as described in the item (1).